Design strategies for shape-persistent covalent organic polyhedrons (COPs) through imine condensation/metathesis

Article abstract of DOI:10.1021/jo3011683

A series of dialdehyde compounds were synthesized and reacted with the complementary triamines (either planar or pyramidal with a 109.5° vertex) in a 3:2 ratio to explore the structural requirements on the building blocks for the successful construction of shape-persistent, covalent organic polyhedrons (COPs). Structural variations in the building blocks included the distance and angle between the two reactive sites (aldehyde or amine functional groups) and the absence/presence of solubilizing chains. Computer modeling was utilized to determine and compare the thermodynamic stabilities of some of these COP structures. Furthermore, gas adsorption studies were performed to explore the potential of these molecular cages for gas separation, particularly carbon capture, applications.

Full text of DOI:10.1021/jo3011683

Article
pubs.acs.org/joc
Design Strategies for Shape-Persistent Covalent Organic
Polyhedrons (COPs) through Imine Condensation/Metathesis
Yinghua Jin,† Athena Jin,† Ryan McCaffrey,† Hai Long,‡ and Wei Zhang*,†
†Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, United States
‡National Renewable Energy Laboratory, Golden, Colorado 80401, United States
S
* Supporting Information
ABSTRACT: A series of dialdehyde compounds were
synthesized and reacted with the complementary triamines
(either planar or pyramidal with a 109.5° vertex) in a 3:2 ratio
to explore the structural requirements on the building blocks
for the successful construction of shape-persistent, covalent
organic polyhedrons (COPs). Structural variations in the
building blocks included the distance and angle between the
two reactive sites (aldehyde or amine functional groups) and
the absence/presence of solubilizing chains. Computer modeling was utilized to determine and compare the thermodynamic
stabilities of some of these COP structures. Furthermore, gas adsorption studies were performed to explore the potential of these
molecular cages for gas separation, particularly carbon capture, applications.
a variety of COPs, some fundamental questions still remain to
be answered, such as what are the criteria for the selection of
building blocks for successful cage formation, particularly for
those shape-persistent, noncollapsible cages? Are there any
requirements for the relative positions (e.g., angle, direction) of
those functional groups in the building units? Is it necessary to
install the solubilizing groups on the starting precursors? Will
the selection of reaction medium affect the product formation?
To gain better understanding on the design rules for COPs, a
systematic study exploring the critical structural parameters
determining the success in COP formation is highly desired.
Design strategies for building blocks of noncovalent assemblies
via metal coordination are well documented,3,4,57 which paves
the way for exploring the construction of 3-D COPs. Herein,
we report the design and syntheses of a series of trigonal
prismatic and football-shaped cage molecules through imine
condensation/metathesis. Such systematic study explores the
dependence of successful COP formation on certain important
structural parameters and will shed some light on the rational
design principle for construction of well-defined COP-based
nanostructures. Additionally, COPII-20 showed a high ideal
selectivity in adsorption of CO2 over N2 (80/1, mol/mol), thus
representing another promising candidate material for carbon
capture applications.
INTRODUCTION
■
In the past two decades, there has been emerging interest in
synthetic molecular cages and their applications.1−7 With the
advent of supramolecular chemistry2,3,6 and dynamic covalent
chemistry,8−11 chemists have been able to gain facile access to a
wide variety of molecular cages, and significant advances have
been made in exploring their applications in the area of
molecular recognition,2,5,12 chemical sensing,13,14 catalysis,15−18
and gas separation and storage.19−21 To date, most molecular
cages have been prepared through self-assembly process driven
by metal−ligand coordination3,4,22 or hydrogen bonding.2,23−27
Chemically and thermally robust covalent organic polyhedrons
(COPs) have also been prepared under dynamic conditions
through imine,21,28−34 borate,35,36 disulfide,37,38 and more
recently, alkyne formation.39,40 However, it still remains a
challenge to synthesize COPs of precise dimensions and shape
with surface functionalities, which is of great importance to
tune the bulk material properties.
Our group has been interested in exploring the possibility of
applying low-density COP21,33 compounds and their cross-
linked framework materials for gas separation,41 especially for
separation of CO2/N2. Extensive studies have been carried out
on zeolites,42,43 metal−organic frameworks (MOFs),44−48 and
covalent organic frameworks (COFs),49−53 all well-established
classes of porous materials, for gas separation and storage.
However, not until recently have discrete organic cages been
introduced as a viable class of novel porous materi-
als.19,21,31,33,54−56 Conventionally, the COPs are synthesized
under irreversible reaction conditions, and usually very low
overall yields are obtained, thus impeding their practical
applications in gas adsorption/separation. Although recent
advances in dynamic covalent chemistry, particularly imine
condensation/metathesis reaction, has promised ready access to
RESULTS
■
Syntheses of Dialdehyde and Triamine Building
Blocks. Dialdehydes 1−7 and triamines 8 and 9 with different
structural and geometrical features (angles and distances
between the two functional moieties) were synthesized. The
Received: June 7, 2012
Published: August 21, 2012
© 2012 American Chemical Society
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pyrene-based dialdehyde building blocks (1, 2a,b) were
synthesized from the 1,8-diethynylpyrene (10).58 Sonogashira
cross-coupling between 10 and several different aromatic
halides afforded dialdehyde building blocks (1, 2a,b, Scheme
1). For compound 2b, the decynyl group was installed to
Scheme 1. Syntheses of Dialdehydes 1 and 2a,b
Table 1. Syntheses of COPs via Imine Condensation/
Metathesis Followed by Reduction
a
ab
,
entry triamine dialdehyde solvent
COP product
yield
enhance the solubility of the precursor and intermediate
oligomers. The tetraphenylmethane-based triamine building
unit (9) was synthesized from the tricarboxylic acid 11.59
Esterification followed by Suzuki cross-coupling provided the
tetradecyl-substituted trimethyl ester 13. Hydrolysis, Curtius
rearrangement, and subsequent amine deprotection provided
triamine 9 (Scheme 2).
1
2
3
4
5
6
7
8
9
8b
8b
8b
8b
8b
8b
8b
8b
8b
8a
9
1
TCB
ND
NA
23
2a
2b
3
TCB
COPI-15a
COPI-15b
ND
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
TCB
83
NA
NA
NA
21
4
ND
5
ND
d
d
d
6a
6b
7
COPI-16a
COPI-16b
COPI-17a
COPI-17b
COPII-18
46
Scheme 2. Synthesis of Triamine 9
74
d
10
11
12
13
14
15
16
17
18
7
75
1
78
c
9
2a
2b
3
TCB
COPII-19a/DTII-19a
trace
c
9
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
COPII-19b/DTII-19b
COPII-20
trace
31
9
9
4
COPII-21
94
9
5
ND
NA
11
9
6a
7
COPII-22
9
COPII-23
69
a
b
c
ND = not detected, NA = not applicable. Isolated yield. Species
with molecular weight corresponding to COPII/DT was observed on
the MALDI mass spectra, Previously described; see refs 21 and 33.
d
(rt) under acid catalysis. Previously, we used Sc(OTf)3 as the
imine metathesis catalyst.21,33 However, we encountered some
complications such as sluggish reactions with aged or different
batches of Sc(OTf)3 from various suppliers. We found a
catalytic amount of trifluoroacetic acid (TFA) provides similar
results as the fresh Sc(OTf)3. In general, 3 equiv of dialdehydes
(1−7) were reacted with 2 equiv of triamine (8a or 8b or 9) in
CHCl3 (or 1,2,4-trichlorobenzene) at room temperature under
the catalysis of TFA. The concentrations of the triamine and
dialdehyde building blocks are 3.0 and 4.5 mM, respectively.
We found the concentration is important: high concentration
leads to fast initial condensation to form insoluble intermediate
oligomeric species; low concentration leads to very sluggish
reaction. Upon formation of the imine-linked COPs,
diisobutylaluminum hydride (DIBAL-H) was added as an
efficient reducing agent to reduce the imine bonds to the
amines at various temperatures.60 Except for entries 1, 2, 6, 7,
Syntheses of COPs. We tested various dialdehydes (1−7)
with the angles between the two reactive aldehyde sites (in the
same plane) ranging from 0° to 300° in imine condensation/
metathesis reaction with triamines 8a, 8b, and 9 to investigate
the design criteria for the building blocks that would lead to
successful cage formations. The results are summarized in
Table 1. In all the attempted syntheses of COPs, the imine
condensation/metathesis was conducted at room temperature
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Figure 1. COP/DT structures observed in this study.
10, and 16, the reaction mixture stayed as a clear solution
throughout the reaction. In all entries, no efforts were made to
remove the condensation byproduct water, and we observed
almost complete conversions of starting materials after 18−24
h. As shown in Table 1, we were able to isolate pure trigonal
prisms (COPI-15a, COPI-15b, COPI-16a, COPI-16b, COPI-
17a, COPI-17b, Figure 1) and elongated molecular triangular
bipyramids (COPII-18, COPII-20, COPII-21, COPII-22, and
COPII-23) in various yield (11−94%). All COP products were
purified by flash column chromatography and characterized by
1H and 13C NMR, GPC, and MALDI-MS (Supporting
Information).
species, presumably higher molecular weight oligomers or
polymers. Although the formation of a higher ordered
dodecahedral imine-linked COP may be possible, we did not
detect any species indicative of its presence in the MALDI-MS
of the reduced reaction mixture. In entry 14, we observed I2 as
another major species in addition to the desired COPII-20, with
a trace amount of higher ordered polyhedron species
(tetrahedron, or interlocked prism). Partially closed inter-
mediates I2 and I3 (Figure 2) were observed as the major
species in the MALDI-MS in entries 4 and 5 even after 3 days
of reaction. Interestingly, in entry 1, we observed mono-triangle
type intermediates I5 and I6 as the major species. Intermediates
I5 (predominant) and I6 were also observed in entries 12 and
13 as the major species along with trace amount of the species
with the correct m/z of the target COPs on MALDI-MS. Thus
the species with the same m/z as the target COP observed in
At the equilibrium, various intermediates were observed in
the failed/low yielding syntheses of COPs. In entries 6 and 16,
the imine condensation/metathesis provided mostly insoluble
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and chemical information encoded into the building blocks. In
the following discussions, we assume sp3 hybridized carbons
have bond angles of ∼109.5° and sp2 hybridized carbons have
bond angles of ∼120°. Planar (8a or b) triamines with 120°
angle between any two amino groups were used in the assembly
of trigonal prismatic cage (Scheme 3, I). Elongated triangular
Scheme 3. Schematic Presentation of the Covalent Assembly
of Molecular Cages
Figure 2. Possible intermediate structures along the pathway to COPs.
Triamine building blocks are blue, and dialdehyde building blocks are
red.
entry 12 and 13 are more likely I7 type double triangle (DT)
instead of the desired cage products. However, we were unable
to isolate them and determine their structures.
Gas Adsorption Study. Previously we have reported the
high selectivity of some COPIs in adsorption of CO2 over
N2.21,33 Under the STP (1 bar, 20 °C) condition, cages COPI-
16b, COPI-17a, and COPI-17b showed a high selectivity of up
to 138/1 (CO2/N2), thus showing great potential in carbon
capture applications. The gas adsorption behavior of the
elongated triangular bipyramidal cages (COPII) containing the
new pyramidal triamine building blocks (9) was investigated by
using cage COPII-20 as a representative example. We measured
the gas adsorption isotherms of amorphous desolvated sample
of COPII-20 as previously described using the custom-built
instrument for low-adsorption-capacity materials.21,41 The gas
adsorption isotherms (Figure 3) show an adsorption capacity
bipyramids are simple variations of triangular prisms, which
could be easily assembled in a similar fashion by using a tritopic
unit with 109.5° angle between the two adjacent amino groups
as a vertex synthon. We selected pyramidal triamine (9) as the
vertex directing the assembly of the proposed elongated
triangular bipyramids (Scheme 3, II). The structural variations
of the dialdehyde building blocks include the absence/presence
of solubilizing chains, the distance and the angle between the
two aldehyde groups, which enabled us to determine what
parameters are critical for successful cage formation. The
isolated yields of COPs were determined after reduction of
imine-linked COPs to more robust amine-linked ones. The
yields were used as an approximate indicator of the actual
degree of imine-linked cage formation, which was also
supported by the GPC characterization of the crude amine
cage product mixtures (Supporting Figures S3−S4)
Geometric Parameters of Building Blocks: Relative
Orientation of Reactive Sites and Conformational
Rigidity. It should be noted that imine bond formation prefers
trans conformation and is rather rigid. Therefore, it can be
considered as “quasi-linear”, similar to a metal−ligand dative
bond. It appears that dynamic covalent approach and
noncovalent assembly via metal coordination share similar
requirements on building block geometries for the successful
COP formation. “Matched” orientation (allowing the formation
of low- or no-strain structures) of the functional groups and
rigidity (enhancing directional effect through “pre-organiza-
tion”) of building blocks are desired for high-yielding synthesis
of COPs.
Figure 3. CO2- and N2-adsorption isotherms at 20 °C for COPII-20.
Inset: N2-adsorption isotherm.
and CO2/N2 selectivity comparable to that of COPI derivatives,
with an adsorption capacity of 2.96 cc/g for CO2 and 0.037 cc/
g for N2, resulting in an ideal adsorption selectivity of 80/1
under the STP condition.61
DISCUSSION
■
With the aim of constructing shape-persistent 3-D COPs, we
selected building blocks containing rigid aromatic moieties in
the backbone with a minimum number of saturated carbons.
Owing to the rigidity of the building units, the shape of the self-
assembled structure is largely determined by the geometrical
Previously we have reported the successful cage formation by
reacting the planar triamine (8b) and the anthracene-based
dialdehyde (7) in chloroform at room temperature.33 After the
hydride reduction, the target amine cage (COPI-17a) was
obtained with a 74% isolated yield. In order to construct COPs
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Table 2. Energy Calculations (kcal/mol) of the Intermediates and COPs
entry
triamine (III)
dialdehyde (IV)
III + IV
I5
I5 + I5 + IV
I4 (n = 2)
I4 + IV
I2
I2 + IV
COP
b
1
37.6
24.8
24.5
10.1
14.5
24.8
24.5
10.1
14.4
62.4
62.1
47.7
52.1
52.4
52.1
37.7
69.4
65.8
59.3
60.2
68.5
48.9
46.0
66.9
163.6
156.1
128.7
134.9
161.8
122.3
102.1
148.2
95.6
99.8
79.2
81.1
95.0
89.1
66.5
71.7
120.4
124.3
89.3
113.2
97.0
84.1
89.2
90.9
85.5
64.4
87.0
138.0
121.5
94.2
139.6
a
b
2/3
4
37.6
117.6 (COPI-15)
b
37.6
106.4
b
5
37.6
95.6
103.7
115.7
110.0
74.5
97.9
c
11
27.6
119.8
113.6
76.6
111.7 (COPII-18)
110.1 (COPII-19)
72.5 (COPII-20)
98.2 (COPII-23)
c
12/13
14
27.6
c
27.6
c
18
27.6
42.0
86.1
101.4
a
b
c
R = H for dialdehyde 2 was used in the calculations. R = H for triamine 8 was used in the calculations. Hydrogen instead of C14H29 alkyl chain for
triamine 9 was used in the calculations.
with larger physical dimensions, the pyramidal triamine 9 was
utilized as the top/bottom building blocks to construct
elongated triangular bipyramid. Stang and co-workers have
reported the self-assembly of similar coordination cages with
D3h symmetry from 1,8-bis(trans-Pt(PEt3)2(NO3))anthracene
and tritopic pyridyl subunits (e.g., tris(4-pyridyl)methanol)
with 109.5° between the two pyridyl binding sites.62
Comparable to the successful formation of Stang’s D3h
supramolecular cages, we were able to obtain COPII-23 from
1,8-diformylanthracene (7) and pyramidal triamine 9 in a
decent yield (69%). The formation of the elongated triangular
bipyramid using triamine 9, which has 109.5° angle between
any two aryl amines, as the two end-caps requires the angle
between the two formyl groups of the dialdehyde connector to
be 39°. However, interestingly, in 1,8-diformylanthracene (7),
the two aldehyde moieties are parallel to each other with the
angle of 0°, which is not a perfect match to the required angle
of 39°. To further probe the range of angles between two
aldehyde moieties of the same building block that allows the
successful COP formation, we tested dialdehydes 1 and 4 with
60° angle, 5 with 180° angle, and 2a-b with 300° angle, in the
imine condensation/metathesis with triamine 9. Covalent
assembly of dialdehyde 1 with triamine 9 provided the desired
molecular cage COPII-18 in a good yield (78%). Similarly, the
reaction between o-phenyleneethynylene-based dialdehyde 4
and triamine 9 also provided an excellent yield (94%) of
COPII-21 (entry 15). However, reactions between dialdehyde 5
with a 180° angle, or dialdehyde 2a−b with a 300° angle
between the two aldehyde groups, and triamine 9 afforded only
a trace amount, if any, of target COPs. The experimental results
suggest the COP formation is tolerant to some degree of
geometry mismatch. However, significant mismatch would
cause energy penalty and prevent the formation of COP
products. The preferential formation of target COPs is
expected when building blocks have least geometry mismatch
and hence least strain. In the assembly of trigonal prisms, since
the angle between the two triangular faces of the target trigonal
prisms is 0°, ideal dialdehyde connectors should have the angle
between the two aldehyde groups close to 0°. Satisfying such
geometrical requirement, dialdehydes 6 and 7 with 0° angle
between the two aldehyde groups formed prismatic cages
(COPI-16a, 16b, 17a) with planar triamine 8b. However, imine
condensation/metathesis of 8b with dialdehydes (1, 3, and 4)
bearing 60° angle between the two aldehyde moieties resulted
in partially closed intermediates (i.e., I2, or I3) without any
noticeable amount of the desired COP structures, presumably
due to the “misalignment” of amine and aldehyde functional
groups. Compared to the planar triamine 8b, pyramidal
triamine 9 appears to be slightly more conformationally flexible
and more tolerant to the geometry mismatch with the
dialdehyde counterparts.
In addition to the angular effect on the covalent assembly
process, we found the conformational rigidity of the building
blocks can also influence the outcome of the self-assembly.
Dialdehydes 3 and 6 have multiple pseudo trans/cis conforma-
tional isomers, which arise from the free rotation of aryl
moieties along the acetylene axis. This conformational flexibility
showed negative effect on the formation of COPs, for example,
entry 11 (COPII-18, 78%) versus entry 14 (COPII-20, 31%).
The two aldehyde groups of 1 in entry 11 are directionally
locked with a favorable 60° angle between them, a
preorganization greatly facilitating the COP formation.
However, in 3 (entry 14), two planar conformational isomers
exist in which the two formyl groups may form a 60° (pseudo-
cis) or 180° (pseudo-trans conformation) angle. Due to the
angle mismatch, the pseudo-trans isomer would promote the
oligomer/polymer side product formation. Therefore, the yield
difference in entry 11 and 14 could be attributed to the better
functional group directionality in dialdehyde 1. To support
such a rationale, dialdehyde 4 that has the same distance and
angle between the two aldehyde groups as in compound 3 but
with better directionality (i.e., two aldehydes groups are locked
into one conformation) was utilized, and the reaction indeed
provided a much higher yield (94%) of the cage product. Such
a notion is further supported by the comparison of entries 8
and 9 (COPII-16b, 46% vs COPI-17a, 74%) and also entries 17
and 18 (COPII-22, 11% vs COPII-23 69%). These results
demonstrate the importance of functional group orientation
(directionality) and rigidity in the molecular cage formation.
Solubility Concern. It should be noted that good solubility
of the building blocks and reaction intermediates is critical to
successful formation of COPs through the dynamic covalent
chemistry. Solvent selection thus appears to be one important
factor. Attempted formation of COPII-18 in CHCl3 resulted in
a large amount of precipitates and provided a complex mixture
of intermediates. In great contrast, reaction in 1,2,4-
trichlorobenzene (TCB), in which dialdehyde 1 has a better
solubility, provided a good yield of COPII-18 (78%, entry 11).
Although Warmuth et al. have reported the formation of
different nanocage products in different solvents, we did not
observe such a solvent effect.63 Another interesting observation
possibly related to the poor solubility issue is the low-yielding
syntheses of COPI-15a (23%) and COPI-16a (21%), the
structural analogues of COPI-15b and COPI-16b, respectively.
The dialdehydes 2a and 6a bear no solubilizing chains, and we
observed a significant amount of precipitation during the
assembly process presumably due to the low solubility of the
reaction intermediates and polymer side products. Therefore,
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when utilizing dynamic covalent chemistry, usually a good
solubility of the intermediate products needs to be maintained
to ensure high-yielding product formation.
functional groups as well as their solubility in the reaction
medium are very important. The alignment of aldehyde and
amino groups in the precursors with an appropriate angle is
highly desired. The presence of certain rotational freedom in
the building blocks can decrease the angle strain built along the
cage formation, thus facilitating the cage synthesis. The
football-shaped molecular cage COPII-20 shows a high ideal
selectivity in adsorption of CO2 over N2 (80/1, v/v), thus
showing great potential, together with other recently developed
COPs, for carbon capture applications.
Computational Study. In the COP synthesis via a
dynamic covalent approach, the product distribution is
determined by the thermodynamic stability of each possible
product at the equilibrium. A large energy gap is required in
order to obtain predominant target structure over other
possible products. In order to illustrate that the energy gap
principle accounts for the high yield of the COP product, we
performed simple calculations on the energies of the building
blocks (triamines III and dialdehydes IV), three possible
intermediates (I2, I4, and I5), and COPs. The energies of the
selected reaction intermediates along the pathway to COPs,
consisting of covalent energies (bond, angle, and torsion) and
noncovalent energies (vdW and electrostatic), were calculated
at the molecular mechanics level and are listed in Table 2. The
covalent interactions in MM are treated as “strings” so that the
energies at the equilibrium position are always zero. To make
the energy comparison easier, for building blocks and
intermediates, the oxygen atom in -CHO or the two hydrogen
atoms in -NH2 were not included. In this way, intermediates
and COPs can be constructed with individual building blocks.
By comparing the energies of COPs (or intermediates) with
ones of corresponding building blocks, the “strain” energy in
molecules was estimated. For each entry, energies of structures
I5 + I5 + IV, I4 + IV, and I2 + IV that contain the same number
of building blocks as a COP, two molecules of triamines and
three molecules of dialdehydes, were compared to the energy of
the desired COP product. Consistent with the experimental
results, in entries 2, 11, and 14, the COP products are
thermodynamically favored and are the predominant species at
the equilibrium. In entries 1, 4, 5, 12, and 13, the corresponding
COP products do not have significantly lower energies
compared to other species, and the reaction did not yield the
target COPs as the predominant and isolable species. In entry
18, intermediate I4 + IV has lower energy than the
corresponding COP. Therefore, the unexpected formation of
COP product could be kinetically determined.
It should be noted that introducing some degree of rotational
freedom into the building blocks could substantially release the
angle strain in the COPs and increase their thermodynamic
stabilities. For example, the aldehyde moieties in dialdehyde 2
have some degree of flexibility through the aryl−aryl single
bond rotation, whereas in dialdehyde 1, the angle is locked to
60°. This slight difference in the structure significantly reduces
the angle strain and lowers the energies of the corresponding
COPs by 21 kcal/mol from 139.6 (entry 1) to 117.6 kcal/mol
(entry 2/3). Therefore, when dialdehyde 2 and 1 reacted with
the same triamine 8b, respectively, 2 formed COPI-15a/b
(entry 2/3), while 1 failed to form the cage (entry 1). The
results suggest introduction of slight conformational flexibility
in the building block design could minimize the buildup of
angle strains during the assembly process without greatly
sacrificing the benefit from the rigidity of the building blocks.
EXPERIMENTAL SECTION
■
Compound 1. Compound 10 (33.8 mg, 0.135 mmol), 4-iodo-
benzaldehyde (126 mg, 0.54 mmol), CuI (0.52 mg, 0.003 mmol), and
Pd(PPh3)2Cl2 (5.7 mg, 0.008 mmol) were placed in a 25-mL Schlenk
tube. The mixture was degassed by evacuating and refilling with
nitrogen three times. THF (3.4 mL) and piperidine (0.05 mL) were
added, and the mixture was stirred at rt for 18 h. The crude reaction
mixture was then concentrated, and the residue was purified by flash
column chromatography (CH2Cl2) to provide compound 1 as a yellow
1
solid (73 mg, 100%): H NMR (400 MHz, CDCl3) δ 10.08 (s, 2H),
8.79 (s, 2H), 8.26 (d, J = 8.0 Hz, 2H), 8.20 (d, J = 8.0 Hz, 2H), 8.12
(s, 2H), 8.01−7.93 (m, 4H), 7.92−7.83 (m, 4H); 13C NMR (75 MHz,
CDCl3) δ 191.6, 135.8, 132.4, 132.3, 132.1, 130.5, 130.0, 129.9, 128.6,
126.8, 125.7, 124.4, 118.1, 95.1, 92.7; HR-MS (ESI) calcd for
C34H18O2 [M + Li+] 465.1468, found 465.1470.
Compound 2a. The general procedure for Sonogashira coupling
described above was followed. Compound 10 (57 mg, 0.23 mmol) was
converted to dialdehyde 2a using CuI (0.86 mg, 0.005 mmol),
Pd(PPh3)2Cl2 (10 mg, 0.014 mmol), 3-bromo-5-iodo-benzaldehyde
(282 mg, 0.91 mmol), THF (6 mL), and piperidine (0.1 mL). The
crude product was purified by flash column chromatography (CH2Cl2)
to give compound 2a as an orange solid (34 mg, 24%): 1H NMR (500
MHz, CDCl3) δ 10.04 (s, 2H), 8.78 (s, 2H), 8.29−8.24 (m, 2H),
8.24−8.18 (m, 2H), 8.15 (s, 2H), 8.14 (s, 2H), 8.12 (s, 2H), 8.04 (s,
2H); 13C NMR (75 MHz, CDCl3) δ 190.3, 139.7, 138.1, 132.2,
132.11, 132.07, 131.6, 130.4, 128.6, 126.72, 126.65, 125.7, 124.3,
123.5, 117.7, 92.9, 91.5; HR-MS (ESI) calcd for C34H16Br2O2 [M +
Li+] 622.9660, found 622.9673.
3-Bromo-5-(1-dodecyn-1-yl)-benzaldehyde. The general pro-
cedure for Sonogashira coupling described above was followed. 3-
Bromo-5-iodo-benzaldehyde (1.0 g, 3.2 mmol) was converted to 3-
bromo-5-(1-dodecyn-1-yl)-benzaldehyde using CuI (6 mg, 0.032
mmol), Pd(PPh3)2Cl2 (68 mg, 0.097 mmol), 1-decyen (2.32 mL,
12.9 mmol), THF (38 mL), and piperidine (4 mL). The crude product
was purified by flash column chromatography (hexanes → EtOAc) to
1
provide the pure product as a brown liquid (1.05 g, 100%): H NMR
(500 MHz, CDCl3) δ 9.92 (s, 1H), 7.90 (t, J = 1.7 Hz, 1H), 7.80 (t, J =
1.4 Hz, 1H), 7.77 (t, J = 1.6 Hz, 1H), 2.45−2.39 (m, 3H), 1.65−1.57
(m, 3H), 1.48−1.41 (m, 3H), 1.36−1.25 (m, 13H), 0.90 (t, J = 7.0 Hz,
5H). 13C NMR (75 MHz, CDCl3) δ 190.2, 139.6, 137.6, 131.6, 130.8,
127.2, 122.9, 94.1, 78.1, 31.8, 29.2, 29.1, 28.9, 28.5, 22.7, 19.4, 14.1;
HR-MS (ESI) calcd for C17H21BrO [M + H+] 321.0849, found
321.0849.
Compound 2b. The general procedure for Sonogashira coupling
described above was followed. Compound 10 (513 mg, 1.6 mmol) was
converted to dialdehyde 2b using CuI (1.5 mg, 0.008 mmol),
Pd(PPh3)2Cl2 (17 mg, 0.024 mmol), 3-bromo-5-(1-dodecyn-1-yl)-
benzaldehyde (100 mg, 0.40 mmol), and triethylamine (5.5 mL). The
crude product was purified by flash column chromatography (50%
CHCl3 in hexane → 75% CHCl3 in hexane) to give compound 2b as
an orange solid (173 mg, 59%): 1H NMR (500 MHz, CDCl3) δ 10.05
(s, 2H), 8.81 (s, 2H), 8.28−8.22 (m, 2H), 8.22−8.17 (m, 2H), 8.14−
8.09 (m, 4H), 7.99 (t, J = 4.6, 3.1 Hz, 2H), 7.90 (t, 2H), 2.46 (t, 4H),
1.71−1.60 (m, 4H), 1.53−1.44 (m, 4H), 1.38−1.28 (m, 16H), 0.89 (t,
J = 7.1 Hz, 6H); 13C NMR (75 MHz, CDCl3) δ 191.2, 139.7, 136.7,
132.4, 131.9, 131.7, 131.3, 130.2, 128.3, 126.5, 126.0, 125.3, 124.9,
124.0, 117.9, 93.8, 93.5, 90.5, 78.9, 32.1, 29.44, 29.36, 29.2, 28.8, 22.9,
SUMMARY
■
A series of imine condensation/metathesis reactions between
planar or pyramidal triamines and dialdehydes was conducted
to explore the critical structural elements required for the
successful shape-persistent COP formation. The experimental
results showed that both the angle and the directionality (e.g.,
two aldehyde groups locked in the same direction) of the
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Article
19.7, 14.4; HR-MS (ESI) calcd for C54H50O2 [M+] 730.3806, found
730.3825.
brine (100 mL), dried over anhydrous Na2SO4, and concentrated to
give the crude product, which contained excess benzyl alcohol. It was
directly hydrolyzed without further purification.
Compound 12. To a solution of the acid 11 (719 mg, 1.25 mmol)
in MeOH (60 mL) was added concentrated H2SO4 (0.7 mL). The
solution was refluxed for 15 h and cooled to rt. The solvent was
evaporated, and water (50 mL) was added. The product was extracted
with CH2Cl2 (3 × 50 mL). The combined organic extracts were dried
over anhydrous Na2SO4 and concentrated to give crude product.
Purification by flash column chromatography (10% CH2Cl2, 8%
EtOAc in hexane) provided the methyl ester 12 (600 mg, 77%):1H
NMR (400 MHz, CDCl3) δ 8.09−7.80 (m, 6H), 7.72−7.49 (m, 2H),
7.31−7.25 (m, 6H), 7.06−6.83 (m, 2H), 3.92 (s, 9H); 13C NMR (101
MHz, CDCl3) δ 166.8, 150.3, 145.0, 137.4, 132.9, 130.9, 129.5, 128.7,
92.9, 65.4, 52.4. The NMR data were consistent with the literature
report by Anderson.59
Compound 13. A solution of 1-tetradecene (485 mg, 2.47 mmol)
in THF (2 mL) was stirred and cooled to 0 °C. 9-BBN (4.94 mL, 0.5
M solution in THF) was added dropwise, and the solution was slowly
warmed to rt. After stirring at rt for 6 h, Pd(PPh3)4 (95 mg, 0.08
mmol) and K2CO3 (453 mg, 3.28 mmol) were added followed by
compound 12 (1.02 g, 1.64 mmol) in DMF (5 mL). The mixture was
heated at 50 °C for 16 h and then cooled to rt. Water (60 mL) was
added, and the reaction mixture was extracted with EtOAc (3 × 60
mL). The combined organic extracts were washed with water (3 × 60
mL) and brine (60 mL), dried over anhydrous Na2SO4, and
concentrated to give the crude product. The residue was purified by
flash column chromatography (10% EtOAc, 10% CH2Cl2 in hexane)
to give the product 13 as a yellow solid (840 mg, 74%): 1H NMR (400
MHz, CDCl3) δ 7.97−7.89 (m, 6H), 7.33−7.28 (m, 6H), 7.09−7.03
(m, 4H), 3.91 (s, 9H), 2.62−2.52 (m, 2H), 1.65−1.59 (m, 2H), 1.36−
1.21 (m, 23H), 0.88 (t, 3H); 13C NMR (75 MHz, CDCl3) δ 166.8,
150.9, 142.0, 141.4, 130.8, 130.6, 129.1, 128.2, 128.0, 65.2, 52.1, 35.4,
31.9, 31.3, 29.7, 29.6, 29.49, 29.45, 29.36, 22.7, 14.1; HR-MS (ESI)
calcd for C45H54O6 [M + H+] 691.3993, found 691.3986.
Step 4: To the solution of the above carbamate in EtOH (40 mL)
was added a solution of KOH (3.07 g, 54.98 mmol) in H2O (4 mL).
The mixture was heated at 95 °C for 18 h. The volatiles were removed
and water (100 mL) was added. The product was extracted with Et2O
(3 × 80 mL). The combined ethereal extracts were washed with brine
(150 mL), dried over Na2SO4, and concentrated to give the crude
product as a pink oil. Purification by flash column chromatography
(20% EtOAc in hexane → 8% MeOH in CH2Cl2) provided the amine
1
9 as a light yellow solid (1.20 g, 57% in four steps): H NMR (500
MHz, CDCl3) δ 7.07 (d, J = 8.4 Hz, 2H), 7.01 (d, J = 8.4 Hz, 2H),
6.97−6.93 (m, 6H), 6.58−6.54 (m, 6H), 3.58 (s, 6H), 2.59−2.49 (m,
2H), 1.63−1.57 (m, 2H), 1.35−1.20 (m, 24H), 0.89 (t, J = 6.9 Hz,
3H); 13C NMR (75 MHz, CDCl3) δ 145.4, 144.0, 140.1, 138.4, 132.2,
131.1, 127.3, 114.2, 62.7, 35.7, 32.2, 31.6, 29.92, 29.88, 29.84, 29.76,
29.7, 29.6, 22.9, 14.4; HR-MS (ESI) calcd for C39H51N3 [M + H+]
562.4156, found 562.4159.
General Procedure for COP Synthesis. To a solution of 8b (20
mg, 0.032 mmol) and 2a (30 mg, 0.049 mmol) in 1,2,4-
trichlorobenzene (TCB) (11 mL) was added a solution of TFA
(0.38 μL, 0.0049 mmol) in CHCl3 (100 μL) slowly dropwise. The
solution was stirred at rt for 18 h, at which time 1H NMR spectrum of
the concentrated crude reaction mixture indicated both of the starting
materials were consumed. DIBAL-H (960 μL, 0.96 mmol, 1.0 M in
CH2Cl2) was added. After stirring at rt for 20 min, the reaction was
quenched with MeOH (1 mL), and saturated NaHCO3 (15 mL) was
added. The mixture was stirred at rt for 30 min, and the organic layer
was separated. The aqueous solution was extracted with CHCl3 (3 ×
30 mL). The combined organics were dried over Na2SO4 and
concentrated to give the crude product. Purification by flash column
chromatography (CH2Cl2) provided the pure product COP-15a as a
1
yellow solid (11 mg, 23%): H NMR (500 MHz, THF) δ 8.79 (br s,
Compound 14. To a suspension of compound 13 (2.57 g, 3.72
mmol) in EtOH (40 mL) was added a solution of KOH (3.12 g, 55.8
mmol) in H2O (12 mL). The mixture was refluxed for 16 h, and
cooled to rt. It was then acidified with HCl (1 N, ∼100 mL) and
extracted with EtOAc (3 × 100 mL). The combined organic extracts
were dried over anhydrous Na2SO4, and concentrated to give
compound 14 as a colorless solid (2.37 g, 98%): 1H NMR (500
MHz, DMSO) δ 7.92 (d, J = 8.4 Hz, 6H), 7.35 (d, J = 8.5 Hz, 6H),
7.19 (d, J = 8.4 Hz, 2H), 7.11 (d, J = 8.4 Hz, 2H), 1.61−1.51 (m, 2H),
1.28−1.23 (m, 24H), 0.87 (t, J = 6.6 Hz, 3H); 13C NMR (101 MHz,
CD3OD) δ 169.4, 152.4, 143.7, 142.6, 132.0, 131.9, 130.3, 130.0,
129.2, 66.4, 36.4, 33.2, 33.1, 32.5, 30.81, 30.79, 30.7, 30.6, 30.5, 30.4,
27.5, 23.8, 23.1, 14.5; HR-MS (ESI) calcd for C42H48O6 [M − H−]
647.3378, found 647.3380.
Compound 9. Step 1: A solution of compound 14 (2.37 g, 3.65
mmol) in CH2Cl2 (20 mL) and THF (5 mL) was stirred and cooled at
0 °C. Oxalyl chloride (4.17 g, 32.9 mmol) was added dropwise,
followed by DMF (3 drops) at 0 °C. The mixture was allowed to warm
to rt and stirred for 1 h. TLC showed all the compound 14 was
consumed. The volatiles were evaporated to give light yellow solid
(2.71 g), which was used in the following step without further
purification.
Step 2: A solution of the above acyl chloride (2.71 g) in acetone
(100 mL) was stirred and cooled to 0 °C, as a solution of NaN3 (2.14
g, 32.9 mmol) in H2O (10 mL) was added dropwise. The mixture was
stirred at 0 °C for 1 h. The solvent was evaporated and water (50 mL)
was added. The organic was separated, and the aqueous layer was
extracted with Et2O (5 × 50 mL). The combined organic extracts were
dried over anhydrous Na2SO4 and concentrated to give the crude
product (3.05 g), which was used in the following step without further
purification
Step 3: To the solution of the above acyl azide (3.05 g) in toluene
(40 mL) was added benzyl alcohol (3.55 g, 32.9 mmol). The solution
was refluxed for 2 h, at which point TLC showed complete conversion
of the acyl azide to carbamate. Ethyl acetate (150 mL) was added, and
the solution was washed with saturated NaHCO3 (2 × 100 mL) and
6H), 8.25 (br s, 12H), 8.15 (br s, 6H), 7.82 (s, 3H), 7.77 (s, 3H), 7.66
(s, 3H), 7.01−6.80 (m, 12H), 6.78−6.49 (m, 12H), 5.53−5.13 (m,
6H), 4.33 (d, J = 4.8 Hz, 12H), 2.17−2.10 (m, 4H), 1.35−0.74 (m,
56H), 0.69 (t, J = 7.3 Hz, 18H); 13C NMR (75 MHz, THF) δ 148.0,
144.7, 140.6, 140.4, 133.6, 133.0, 132.9, 132.1, 131.9, 131.8, 131.0,
130.7, 129.3, 127.4, 126.5, 126.4, 125.2, 123.2, 119.2, 113.1, 95.3, 90.3,
48.7, 33.1, 32.0, 31.3, 30.8, 30.6, 30.5, 30.0, 23.7, 23.3, 14.8, 14.6; MS
(MALDI) calcd for C186H162Br6N6 ([M+]) 2960.80, found 2960.75.
COPI-15b. The general procedure for COP synthesis described
above was followed. Compound 8b (11 mg, 0.018 mmol) and 2b (20
mg, 0.027 mmol) were converted to COPI-15b (25 mg, 83%, a yellow
solid) using TFA (0.21 μL, 0.0027 mmol), CHCl3 (6 mL), and
DIBAL-H (540 μL, 0.54 mmol, 1.0 M in CH2Cl2, 0 °C). The physical
1
data for COPI-15b: H NMR (500 MHz, CDCl3) δ 8.79 (br s, 6H),
8.24−8.19 (m, 6H), 8.18−8.14 (m, 6H), 8.09 (s, 6H), 7.80 (br s, J =
13.1 Hz, 6H), 7.68 (br s, 6H), 7.48 (br s, J = 8.8 Hz, 6H), 7.16 (br s,
6H), 6.68 (s, 18H), 4.29 (s, 12H), 3.81 (s, 6H), 2.44 (t, J = 7.1 Hz,
12H), 2.17−2.07 (m, 12H), 1.66−1.60 (m, 12H), 1.51−1.45 (m,
12H), 1.38−1.24 (m, 72H), 1.24−1.15 (m, 12H), 1.06−1.00 (m,
12H), 0.89 (t, J = 6.8 Hz, 18H), 0.76 (t, J = 7.3 Hz, 18H); 13C NMR
(75 MHz, CDCl3) δ 146.4, 140.1, 139.9, 139.2, 133.9, 132.2, 132.0,
131.7, 131.3, 130.8, 128.3, 126.8, 125.4, 125.1, 124.4, 124.1, 118.6,
112.8, 95.3, 91.8, 89.2, 80.0, 49.1, 32.1, 31.2, 29.9, 29.8, 29.5, 29.4,
29.2, 29.0, 22.9, 22.6, 19.7, 14.44, 14.36; MS (MALDI) calcd for
C246H264N6 ([M+]) 3304.09, found 3304.04.
COPII-18. The general procedure for COP synthesis described
above was followed. Compound 9 (15 mg, 0.027 mmol) and
compound 1 (18 mg, 0.040 mmol) were converted to COPII-18 (a
light yellow solid, 25 mg, 78%) using TFA (0.31 μL, 0.004 mmol),
CHCl3 (9 mL), and DIBAL-H (810 μL, 0.81 mmol, 1.0 M in CH2Cl2).
The physical data for COPII-18: 1H NMR (500 MHz, CDCl3) δ 8.98
(s, 6H), 8.10 (d, J = 14.6 Hz, 6H), 7.69 (d, J = 9.0 Hz, 6H), 7.62 (d, J
= 13.1 Hz, 6H), 7.57 (d, J = 8.0 Hz, 12H), 7.52 (d, J = 8.2 Hz, 6H),
7.36 (d, J = 8.7 Hz, 12H), 7.12−7.09 (d, 6H), 7.07 (d, J = 7.9 Hz,
12H), 6.37 (d, J = 13.7 Hz, 12H), 3.85 (br s, 12H), 3.22 (br s, 6H),
2.58−2.45 (m, 4H), 1.61−1.54 (m, 4H), 1.37−1.15 (m, 44H), 0.92 (t,
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The Journal of Organic Chemistry
Article
J = 6.9 Hz, 6H); 13C NMR (101 MHz, Toluene) δ 147.0, 146.7, 141.5,
140.5, 138.6, 138.2, 137.6, 133.01, 133.0, 132.6, 132.3, 132.2, 130.4,
128.2, 128.0, 127.4, 125.4, 123.2, 119.8, 112.8, 96.8, 89.5, 63.8, 48.9,
32.7, 32.1, 30.6, 30.50, 30.48, 30.4, 30.3, 30.2, 23.4; MS (MALDI)
calcd for C180H156N6 ([M+]) 2402.24, found 2401.33.
ASSOCIATED CONTENT
■
S
* Supporting Information
Materials and general synthetic methods, GPC graphs,
computational method, and NMR spectra of compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
COPII-20. The general procedure for COP synthesis described
above was followed. Compound 9 (500 mg, 0.89 mmol) and 3 (313
mg, 1.33 mmol) were converted to COPII-20 (239 mg, 31%, a light
yellow solid) using Sc(OTf)3 (66 mg, 0.13 mmol), CHCl3 (300 mL),
and NaBH(OAc)3 (5.66 g, 26.7 mmol). The physical data for COPII-
20: 1H NMR (500 MHz, CDCl3) δ 7.57 (s, 6H), 7.44−7.40 (m, 6H),
7.32−7.29 (m, 12H), 7.13−7.07 (m, 4H), 7.06−6.99 (m, 4H), 6.95
(br d, J = 8.8 Hz, 12H), 6.49 (br d, J = 7.5 Hz, 12H), 4.29 (s, 12H),
4.00 (s, 6H), 2.59−2.53 (m, 4H), 1.64−1.58 (m, 4H), 1.33−1.24 (m,
44H), 0.89 (t, J = 8.6 Hz, 6H); 13C NMR (75 MHz, CDCl3) δ 145.7,
145.6, 140.3, 140.0, 137.6, 132.2, 131.1, 130.9, 130.4, 128.8, 127.6,
127.2, 123.7, 111.9, 89.7, 62.6, 48.4, 35.7, 32.2, 31.6, 29.93, 29.89,
29.85, 29.78, 29.7, 29.6, 22.9, 14.4; MS (MALDI) calcd for C126H132N6
([M+]) 1730.05, found 1729.48.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: wei.zhang@colorado.edu.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Dr. Bret Voss for gas adsorption measurement,
National Science Foundation (DMR-1055705) for funding
support. Acknowledgment is also made to the donors of the
American Chemical Society Petroleum Research Fund for
partial support of this research. This research used capabilities
of the National Renewable Energy Laboratory Computational
Science Center, which is supported by the Office of Energy
Efficiency and Renewable Energy of the U.S. Department of
Energy under Contract No. DE-AC36-08GO28308.
COPII-21. The general procedure for COP synthesis described
above was followed. Compound 9 (20 mg, 0.036 mmol) and
compound 4 (18 mg, 0.054 mmol) were converted to COPII-21 (a
light yellow solid, 34 mg, 94%) using TFA (0.42 μL, 0.005 mmol),
CHCl3 (12 mL), and DIBAL-H (1.08 mL, 1.08 mmol, 1.0 M in
CH2Cl2). The physical data for COPII-21: 1H NMR (500 MHz,
CDCl3) δ 7.56 (dd, J = 5.8, 3.4 Hz, 6H), 7.54 (d, J = 8.2 Hz, 12H),
7.33 (d, J = 8.6 Hz, 12H), 7.31 (dd, J = 6.1, 2.7 Hz, 6H), 7.10 (d, J =
8.2 Hz, 4H), 7.04−6.96 (m, 16H), 6.52 (d, J = 8.6 Hz, 12H), 4.27 (s,
12H), 3.92 (s, 6H), 2.60−2.50 (m, 4H), 1.67−1.52 (m, 4H), 1.39−
1.19 (m, 44H), 0.89 (t, J = 7.0 Hz, 6H); 13C NMR (75 MHz, CDCl3)
δ 145.8, 145.5, 140.3, 140.1, 137.7, 132.2, 132.1, 131.7, 131.1, 128.2,
127.9, 127.3, 126.3, 122.4, 111.9, 93.8, 88.6, 62.6, 48.7, 35.7, 32.2, 31.6,
29.93, 29.89, 29.85, 29.77, 29.75, 29.6, 22.9, 14.4; MS (MALDI) calcd
for C150H144N6 ([M+]) 2030.15, found 2030.32.
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■
COPII-22. The general procedure for COP synthesis described
above was followed. Compound 9 (49 mg, 0.087 mmol) and
compound 6b (96 mg, 0.130 mmol) were converted to COPII-22 (a
light yellow solid, 15 mg, 11%) using TFA (1.0 μL, 0.013 mmol),
CHCl3 (30 mL), and DIBAL-H (2.61 mL, 2.61 mmol, 1.0 M in
CH2Cl2). The physical data for COPII-22: 1H NMR (500 MHz,
CDCl3) δ 7.51 (s, 6H), 7.41 (br s, J = 10.8 Hz, 6H), 7.36 (s, 6H), 7.24
(br s, J = 19.8 Hz, 3H), 7.09 (br d, J = 7.7 Hz, 4H), 7.03−6.93 (m,
22H), 6.45 (d, J = 7.3 Hz, 12H), 4.24 (d, J = 25.1 Hz, 12H), 3.96 (app
t, J = 6.4 Hz, 12H), 2.55−2.48 (m, 4H), 1.86−1.68 (m, 4H), 1.59−
1.50 (m, 4H), 1.47−1.41 (m, 4H), 1.32−1.22 (m, 120H), 0.90−0.87
(m, 15H); 13C NMR (101 MHz, CDCl3) δ 13C NMR (101 MHz,
CDCl3) δ 159.1, 145.3, 142.6, 140.2, 137.8, 135.2, 133.1, 132.1, 131.1,
130.7, 129.4, 127.8, 127.3, 125.1, 124.2, 122.5, 118.1, 112.1, 89.9, 88.5,
68.6, 47.7, 35.7, 32.2, 31.6, 29.94, 29.90, 29.86, 29.8, 29.8, 29.6, 29.4,
26.2, 22.9, 14.37; MS (MALDI) calcd for C198H235Br6N6O3 ([MH+])
3226.34, found 3226.71
COPII-23. The general procedure for COP synthesis described
above was followed. Compound 9 (45 mg, 0.080 mmol) and 7 (28 mg,
0.120 mmol) were converted to COPII-23 (48 mg, 69%, a yellow
solid) using TFA (0.92 μL, 0.012 mmol), CHCl3 (27 mL), and
DIBAL-H ((2.43 mL, 2.43 mmol, 1.0 M in CH2Cl2, −40 °C). The
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Wibowo, A. C.; Smith, M. D.; Krause, J. A.; Pellechia, P. J.; Shimize, L.
S. J. Am. Chem. Soc. 2011, 133, 7025−7032.
1
physical data for COPII-23: H NMR (500 MHz, CDCl3) δ 9.03 (s,
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3H), 8.49 (s, 3H), 7.98 (d, J = 8.5 Hz, 6H), 7.53 (d, J = 6.6 Hz, 6H),
7.43 (dd, J = 8.3, 6.9 Hz, 6H), 7.12 (d, J = 8.1 Hz, 4H), 7.06−6.98 (m,
16H), 6.52 (d, J = 16.6 Hz, 12H), 4.74 (s, 12H), 3.91 (br s, J = 54.6
Hz, 6H), 2.56 (dd, J = 20.9, 13.2 Hz, 4H), 1.58 (quint, J = 14.7, 7.2
Hz, 4H), 1.32−1.26 (m, 48H), 0.89 (t, J = 6.9 Hz, 6H); 13C NMR
(101 MHz, CDCl3) δ 146.3, 145.8, 139.9, 137.5, 135.8, 132.3, 132.2,
131.2, 130.2, 128.6, 127.9, 127.2, 126.5, 125.4, 120.0, 111.7, 62.6, 48.1,
35.7, 32.1, 31.6, 29.92, 29.88, 29.84, 29.77, 29.6, 22.9, 14.4; MS
(MALDI) calcd for C126H133N6 ([MH+]) 1731.05, found 1731.15
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